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[SPARK-17271] [SQL] Planner adds un-necessary Sort even if child ordering is semantically same as required ordering #14841

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[SPARK-17271] [SQL] Planner adds un-necessary Sort even if child ordering is semantically same as required ordering #14841

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3 changes: 3 additions & 0 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SortOrder.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,9 @@ case class SortOrder(child: Expression, direction: SortDirection)
override def sql: String = child.sql + " " + direction.sql

def isAscending: Boolean = direction == Ascending

def semanticEquals(other: SortOrder): Boolean =
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@cloud-fan cloud-fan Sep 1, 2016

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Expression has a default implementation of semanticEquals, doesn't it work?

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@tejasapatil tejasapatil Sep 1, 2016

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@cloud-fan : If you look at the old version of EnsureRequirements below at L253, it compared raw SortOrder objects which will use equals() generated for it. In scala, equals() for case classes is merely doing equals() over all its fields so that lead to Expression's equals() being used instead of its semanticEquals().

My fix here was to introduce a semanticEquals in SortOrder which compares the underlying Expression semantically.

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@cloud-fan cloud-fan Sep 1, 2016 •
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yea I understand in EnsureRequirements we should use semanticEquals instead of == to compare SortOrder, but why we need to implement samanticEquals again in SortOrder? What's wrong with the default implementation?

I mean, there is no need to "introduce" a semanticEquals in SortOrder, it already has, because SortOrder is also Expression

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@tejasapatil tejasapatil Sep 1, 2016

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@cloud-fan : I see what you were trying to say before. I tried that and it worked. I have created a PR to clean it up : #14910 Thanks for pointing this out !!

(direction == other.direction) && child.semanticEquals(other.child)
}

/**
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11 changes: 10 additions & 1 deletion sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala
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Expand Up @@ -250,7 +250,16 @@ case class EnsureRequirements(conf: SQLConf) extends Rule[SparkPlan] {
children = children.zip(requiredChildOrderings).map { case (child, requiredOrdering) =>
if (requiredOrdering.nonEmpty) {
// If child.outputOrdering is [a, b] and requiredOrdering is [a], we do not need to sort.
if (requiredOrdering != child.outputOrdering.take(requiredOrdering.length)) {
val orderingMatched = if (requiredOrdering.length > child.outputOrdering.length) {
false
} else {
requiredOrdering.zip(child.outputOrdering).forall {
case (requiredOrder, childOutputOrder) =>
requiredOrder.semanticEquals(childOutputOrder)
}
}

if (!orderingMatched) {
SortExec(requiredOrdering, global = false, child = child)
} else {
child
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40 changes: 39 additions & 1 deletion sql/core/src/test/scala/org/apache/spark/sql/execution/PlannerSuite.scala
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Expand Up @@ -20,7 +20,7 @@ package org.apache.spark.sql.execution
import org.apache.spark.rdd.RDD
import org.apache.spark.sql.{execution, DataFrame, Row}
import org.apache.spark.sql.catalyst.InternalRow
import org.apache.spark.sql.catalyst.expressions.{Ascending, Attribute, Literal, SortOrder}
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.Inner
import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Repartition}
import org.apache.spark.sql.catalyst.plans.physical._
Expand Down Expand Up @@ -444,6 +444,44 @@ class PlannerSuite extends SharedSQLContext {
}
}

test("EnsureRequirements skips sort when required ordering is semantically equal to " +
"existing ordering") {
val exprId: ExprId = NamedExpression.newExprId
val attribute1 =
AttributeReference(
name = "col1",
dataType = LongType,
nullable = false
) (exprId = exprId,
qualifier = Some("col1_qualifier")
)

val attribute2 =
AttributeReference(
name = "col1",
dataType = LongType,
nullable = false
) (exprId = exprId)

val orderingA1 = SortOrder(attribute1, Ascending)
val orderingA2 = SortOrder(attribute2, Ascending)

assert(orderingA1 != orderingA2, s"$orderingA1 should NOT equal to $orderingA2")
assert(orderingA1.semanticEquals(orderingA2),
s"$orderingA1 should be semantically equal to $orderingA2")

val inputPlan = DummySparkPlan(
children = DummySparkPlan(outputOrdering = Seq(orderingA1)) :: Nil,
requiredChildOrdering = Seq(Seq(orderingA2)),
requiredChildDistribution = Seq(UnspecifiedDistribution)
)
val outputPlan = EnsureRequirements(spark.sessionState.conf).apply(inputPlan)
assertDistributionRequirementsAreSatisfied(outputPlan)
if (outputPlan.collect { case s: SortExec => true }.nonEmpty) {
fail(s"No sorts should have been added:\n$outputPlan")
}
}

// This is a regression test for SPARK-11135
test("EnsureRequirements adds sort when required ordering isn't a prefix of existing ordering") {
val orderingA = SortOrder(Literal(1), Ascending)
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